The present invention relates generally to the field of investment casting. In particular, the invention relates to collecting and removing particles in investment casting slurry tanks.
In the investment casting industry, large slurry tanks with circulating ceramic slurry are used to coat injection molded wax patterns with ceramic. These slurry tanks are open to the environment and are typically used for weeks at a time. Wax patterns are assembled into a mold assembly. Typically, this assembly contains: gating, the wax pattern, and a pour cone. This assembly is then repeatedly dipped into the slurry tanks using a manual or automatic dipping process. After the ceramic slurry and stuccos have been adequately coated onto the wax pattern to create a ceramic shell, the wax is removed and metal is cast into the void in the ceramic shell left by the wax. After casting, the ceramic shell is then removed, leaving the cast metal part.
Because the slurry tanks are open to the environment, one problem that occurs as time progresses is that the water in the slurry tank begins to evaporate. Ceramic particles then agglomerate together and dry, forming a layer of dried ceramic agglomerates on the wall surfaces of the slurry tank and on the mixing blade (Z-bar) of the slurry tank. As moisture continues to evolve, dried ceramic builds up on the walls, the weight of the ceramic agglomerates can no longer be supported and the ceramic agglomerates fall into the ceramic slurry, creating debris within the slurry tank. Over time, large amounts of dried ceramic debris build up in the slurry tank, and as the slurry tank circulates the ceramic slurry, the dried debris continues to be stirred up in the slurry tank without being redispersed into the ceramic slurry.
Thus, when the molds are initially dipped into the ceramic slurry, the agglomerates also adhere to the surface of the wax pattern, forming defects. The defects are a result of the ceramic slurry not smoothly covering the surface of the mold due to the agglomerates. These agglomerates can form defects such as, but not limited to: excessive surface roughness, metal fining, positive metals, and inclusions. In order to smooth out the defects, additional processing after the mold has been cast is necessary during the finishing operations. It is therefore important to obtain a smooth and uniform surface on the initial dip into the ceramic slurry.
A current method of collecting and removing the ceramic debris from the slurry tanks is to manually scoop the ceramic debris from the ceramic slurry using a small hand-held screen. Due to the excessive agglomerate build up, the ceramic slurry in the slurry tanks have a lifetime of approximately a quarter of a year before the ceramic slurry must be discarded and replaced. Each time the ceramic slurry must be removed from the slurry tank, the slurry tanks must be cleaned, creating time and labor costs.